1. Field of the Invention
The present invention relates to a thin-film capacitor suitable for a decoupling capacitor and a manufacturing method of the same.
2. Description of the Related Art
Conventionally, a circuit wiring board mounts a decoupling capacitor of a stacked chip structure in the vicinity of a semiconductor integrated circuit element thereof as a measure to prevent the semiconductor integrated circuit element from malfunction due to power supply voltage variation and high frequency noise in the substrate. Specifically, the decoupling capacitor is used in electric equipment for a computer or the like.
Further, along with increasing speed and lowering electric power consumption of the semiconductor integrated circuit element in recent years, performance improvement has been demanded in view of capacitance, high-frequency following and so forth. As a capacitor to respond to the demand as described above, a thin-film capacitor making use of a microfabrication technology for a thin film has been developed. The thin-film capacitor is generally composed of two electrode thin films formed on a substrate and a dielectric thin film formed therebetween.
The thin-film capacitor of the above-described type is capable of reducing the distance between the electrodes by the microfabrication, allowing obtaining a structure having low inductance in the high frequency zone.
In addition, a flip-chip bonding using a solder bump is performed as a technology to mount the thin-film capacitor in the vicinity of the semiconductor integrated circuit element on the circuit wiring board with high reliability and at low cost (Patent Application Laid-Open No. 2004-079801 and Japanese Patent Application Laid-Open No. 2001-338836).
Here, the description will be given of a conventional thin-film capacitor with reference to FIG. 11. FIG. 11 is a sectional view showing a structure of the conventional thin-film capacitor. Note that FIG. 11 shows only the vicinity of the solder bump for a bottom electrode.
In the conventional thin-film capacitor, a SiO2 film 52 is formed on a silicon substrate 51 and a TiO2 film 53 is formed thereon as an adhesive film. On the TiO2 film 53, further, a Pt bottom electrode 54, a BST dielectric film 55 and an Au top electrode 56 are stacked sequentially. The Pt bottom electrode 54, the BST dielectric film 55 and the Au top electrode 56 compose a thin-film capacitor element. Note that the BST dielectric film 55 and the Au top electrode 56 have an opening exposing the Pt bottom electrode 54, respectively.
Further, an Al2O3 protective film 57 and a polyimide protective film 58 having photosensitivity are stacked sequentially all over the surface. With the Al2O3 protective film 57, moisture or the like is prevented from entering into the thin-film capacitor element from the polyimide protective film 58 being an organic protective film. Note that the Al2O3 protective film 57 and the polyimide protective film 58 respectively have an opening 59 exposing the Pt bottom electrode 54 from the center of the opening of the BST dielectric film 55 and the Au top electrode 56.
In the opening 59, a Ti film 60 as a base electric conductor and a Cu film 61 serving as a plating seed layer as well as a solder-resistant barrier layer are formed. Further, on the Cu film 61, an Ni plating film 62 filling the opening 59 is formed as a solder barrier layer. Finally, on the Ni plating film 62, a solder bump 63 made of Sn—Ag is formed. When forming the solder bump 63, a solder plating film made of Sn—Ag is formed, and after that, wet back (ball up) is performed to the solder plating film.
The thickness of the respective films composing the thin-film capacitor is about 100 nm and the thickness of the solder plating film is about 70 μm to 100 μm. Therefore, when performing the wet back of the solder plating film (ball up of the plating film) and when mounting to the circuit wiring board, large stress is applied to the respective films composing the thin-film capacitor, in which a peal-off of the film is sometimes caused in the thin-film capacitor.